The company said the attack works best on Google’s Nexus 5 with stock ROM, and with some modifications for HTC’s One, LG’s G3 and Samsung’s S5.

The attack is an extension of other ones developed for CVE-2015-3864, a remote code execution vulnerability patched twice by Google.

Security company Zimperium found the original Stagefright flaws in early 2015, which affected millions of devices. Google has since repeatedly issued patches and fixes for problems in Stagefright that researchers continue to find.

At issue is NorthBit’s research paper provides details for professional hacking groups to complete a fully working exploit.

NorthBit also published a video of a successful attack, which requires a bit of social engineering. The victim has to be tricked into clicking on a link and then staying on that Web page for some time while the exploit runs. It can take between a few seconds to up to two minutes for the exploit to finish its work.

In the video, the victim, who is using a Nexus 6, opens a link leading to cat photos, while NorthBit shows the exploit churning away.

On Android versions 5.0 and 5.1, the exploit will bypass ASLR (address space layout randomization), a defense intended to make exploitation more difficult.

NorthBit estimated about 235 million Android devices run versions 5.0 and 5.1, and about 40 million devices run some 2.x version of Android without ASLR.

“Looking at these numbers, it’s hard to comprehend how many devices are potentially vulnerable,” NorthBit said.